YES(?,O(n^2))
TRS:
 {
    average(x, s s s y) -> s average(s x, y),
        average(s x, y) -> average(x, s y),
  average(0(), s s 0()) -> s 0(),
    average(0(), s 0()) -> 0(),
      average(0(), 0()) -> 0()
 }
 DUP: We consider a non-duplicating system.
  Trs:
   {
      average(x, s s s y) -> s average(s x, y),
          average(s x, y) -> average(x, s y),
    average(0(), s s 0()) -> s 0(),
      average(0(), s 0()) -> 0(),
        average(0(), 0()) -> 0()
   }
  Matrix Interpretation:
   Interpretation class: triangular
         [0]
   [0] = [3]
   
       [X1]    [1 0][X1]   [2]
   [s]([X0]) = [0 1][X0] + [1]
   
             [X3]  [X1]    [1 1][X3]   [1 0][X1]   [0]
   [average]([X2], [X0]) = [0 1][X2] + [0 1][X0] + [2]
   
   
   Qed